1. Field of the Invention
The present invention relates to a process of grafting a vinyl polymeric material onto an inorganic substrate utilizing ceric ion as the reaction initiator. The invention also relates to the product obtained from said process.
2. Description of the Prior Art
Polymeric materials are composed of long chains of one or more monomeric elements covalently bonded together to form a macromolecule. Examination of a homopolymer or random copolymer at the microscopic level reveals that over a sufficiently long segment, the composition and structure of the segments are essentially constant and independent of the respective monomer positions along the chain. This relative homogeneity is in direct contrast to the heterogeneity of those macromolecules known as block or graft copolymers. These macromolecules involve two or more long homogenous segments covalently bonded to adjacent homogeneous segments which differ in either composition or structure. When such segments are arranged in linear arrays, the macromolecule is termed a block polymer; when the segments form a branched structure involving a main chain to which are attached side chains of a different composition, the macromolecule is termed a graft polymer.
Graft polymerization depends on the creation of active sites on the substrate. In general, there are three approaches to creating these active sites so that graft polymerization can occur: chain-transfer activation, radiation or photochemical activation, and chemical activation. Both chain transfer and chemical activation can be applied to either radical or ionic graft polymerization methods.
In chain-transfer grafting, a mixture of three products is formed: unmodified backbone polymer, graft copolymer, and homopolymer of the monomer to be grafted. This mixture is particularly troublesome in chain-transfer grafting because the grafting efficiency is a function of a large number of variables, such as the type of initiator, the particular structure of the substrate, the type of monomer, the ratio of reactants and the reaction conditions.
Activation grafting is the creation of active sites on the substrate by the absorption of radiant energy. Either ultra-violet light or high energy radiation can be used as the energy source. The activation can be conducted as preirradiation of the polymeric substrate or as mutual irradiation of the polymeric substrate and the monomer to be grafted. By either method, the rate and efficiency of the initiation is dependent upon the type of radiation, the radiation dose (total energy absorbed), the dose rate (rate at which energy is absorbed), and the radiation sensitivity of materials involved. Generally, the radiation dose determines the number of grafted chains, while the dose determines the chain lengths.
Chemical grafting is the term applied to grafting reactions involving preformed labile groups either on the backbone or on pendant groups of the substrate, and can be used in the preparation of graft polymers by either free radical or ionic methods.
In free radical-initiated chemical grafting, active sites are often created as a result of a hydrogen abstraction reaction. The polymerization reaction is thus initiated directly by a polymer chain radical, and when unsaturated monomer is present, polymerization occurs, resulting in the newly formed polymer being covalently bonded or grafted onto the existing polymer molecule.
One of the more widely investigated free radical chemical grafting techniques depends on the redox reaction of certain salts with organic reducing agents. This reaction proceeds by a single electron transfer with the formation of organic free radicals. For example, the patent to Mino et al., U.S. Pat. No. 2,922,768 teaches the polymerization of vinyl monomers in the presence of ceric salt with organic reducing agents, such as alcohols, aldehydes, thiols glycols, and amines. If a polymeric reducing agent such as poly (vinyl alcohol) or cellulose is employed, and the oxidation is conducted in the presence of a vinyl or olefin monomer, graft polymerization will occur on the substrate.
The ceric ion grafting technique is applicable to a large variety of polymeric backbones, both natural and synthetic. Characteristic of effective backbone polymers are polygalactosides such as carrageenans, and an even greater variety among synthetic polymers since these can be tailored to include a reactive group.
Ceric ion initiated graft polymerization has been utilized in conjunction with a large number of hydroxyl, thiol, and amine containing polymeric substrates, including cellulose and starch. Cellulose is readily abundant raw material, but its properties are such that it cannot be used directly. Due to its extremely strong hydrogen bonding forces, it is highly crystalline in nature, insoluble in most solvents, and decomposes at high temperatures without flowing or melting.
Although similar to cellulose in structure, when a water slurry of starch is heated to near boiling, the hydrogen bonds are broken, and a smooth dispersion results. Both starch and cellulose are polymers of glucose in which the glucose units are joined together by glucoside linkages at carbons 1 and 4. The two polysaccharides differ only in the configuration at carbon 1.
The formation of small amounts of homopolymer during ceric ion grafting is well known. Although many of the monomers capable of being grafted onto cellulose via ceric ion initiation undergo ceric ion initiated homopolymerization in the absence of cellulose or similar substrates, there is a marked decrease in reaction rate, yield, and molecular weight of the polymer.
The graft copolymerization of vinyl monomers onto cellulose in the presence of ceric salts proceeds readily when the monomer is a polar electron acceptor monomer such as acrylonitrile or ethyl acrylate; nonpolar hydrocarbon electron donor monomers such as butadiene or styrene which readily undergo radical polymerization graft onto cellulose only with difficulty or under special conditions. The same type of grafting activity is observed when starch is the substrate polymer with respect to the monomers which will graft.
The prior art is prolific with reference to certain polymeric materials which are distinguishable from the product and the process of the present invention. For example, U.S. Pat. No. 2,738,740 discloses polymeric compositions of ethylenically unsaturated compounds which contains or which may be coated upon an inorganic siliceous solid which is chemically bonded to the polymer through a siloxy oxygen linkage. Clays, such as attapulgite and bentonite are included in the inorganic siliceous solid classification. However, these materials must be acid treated in order to be activated. The patent discloses ethylenically-unsaturated monomers which are not polymerized directly onto the inorganic solid, but rather to an unsaturated ester which has been chemically bonded to the solid by esterifying it with an unsaturated alcohol.
U.S. Pat. No. 2,795,545 discloses the formation of an adduct between inorganic hydrophilic solids having high surface areas and cationic polymers. Once such an adduct is formed, free polymeric material cannot be extracted with the solvent for the polymer. Preferred inorganic solids include naturally occurring clayey substances containing large proportions of montmorillonite and cationic polymers including polymers of various pyridines, amides, an amines.
U.S. Pat. No. 2,865,880 teaches the polymerization of acrylonitrile in the presence of colloidal aluminum and silicon oxides using peroxide initiators such that the resulting polyacrylonitrile contains colloidal aluminum and silicon oxides uniformly dispersed throughout.
U.S. Pat. No. 2,967,168 discloses a process for preparing silica containing chemically bonded vinyl groups by cohydrolyzing a vinylchlorosilane and silicon tetrahalide in an aqueous solution. The vinyl modified silica areogel is subsequently copolymerized with unsaturated monomeric materials using a peroxide initiator to yield copolymers in which the silica is an intergral part of the polymer. This disclosure differs substantially from the invention as disclosed in the present application in that the inorganic solid is chemically bonded to an unsaturated monomeric material in a process separate from the polymerization process. Additionally, this reference does not utilize acidic initiator to initiate the polymerization process.
U.S. Pat. No. 3,068,158 teaches the adsorption of a free radical-forming initiator on the surface of a clay mineral. The catalyst-treated clay is dispersed in a fluid medium. Thereafter, an ethylenically unsaturated monomer capable of being polymerized by said catalyst is added, and the reaction mixture is polymerized. The final polymeric product is a dispersion of essentially discrete particles of clay having a surface film of polymer. The free radical initiators include organic and inorganic peroxides, organic percarbonates, and certain azo compounds. It should be noted that in applicant's invention, the inorganic clayey substrate is not brought into contact with the free radical initiator prior to adding the unsaturated monomer.
U.S. Pat. No. 3,208,984 discloses the formation of an adduct between any solid which undergoes an ion exchange type of reaction with organic compounds containing basic nitrogen and an organic azo compound having at least one basic nitrogen radical. The preferred solid substrates are naturally occurring alumino-silicate clays which must be acid treated prior to reaction. The acid clay-organic azo adduct is then used as a free radical initiator for ethylenically unsaturated monomers which results in the formation of polymeric chains which are chemically bonded to the solid substrate surface. In the present invention, the clayey substrate is not acid treated prior to reaction.
U.S. Pat. No. 3,272,749 discloses the graft polymerization of an ethylenically unsaturated monomeric material which may be made water soluble by hydrolysis onto a poly (vinyl alcohol) substrate using a ceric salt initiator. The disclosure is limited to the use of an organic substrate.
U.S. Pat. No. 3,318,826 discloses a clayey substance which is treated to bind ferrous iron by ion exchange. The clay then is mixed with a styrene monomer. After heating, the clay will contain a polymer anion.
U.S. Pat. No. 3,346,535 discloses the base exchanging of a suitable polymerization initiator onto carbon and subsequent employment of the carbon-initiator complex to initiate polymerization of a suitable vinyl monomer and thereby graft propagate a polymeric chain from the carbon atom. Suitable polymerization initiators must have one or more cationic groups capable of ionically bonding to carboxylic acid radical of the carbon. Preferred initiators include heterocyclic azo initiators which minimize the formation of homopolymer. The vinyl monomer is added and heat is applied to create free radicals from the bound azo initiator, which subsequently cause graft polymerization of the monomer onto the carbon substrate.
U.S. Pat. No. 3,557,038 discloses the graft polymerization of diacetone acrylamide with or without an unsaturated comonomer onto the surface of a siliceous solid using a peroxy compound capable of initiating a free radical polymerization.
Surprisingly, I have discovered that certain inorganic substrates such as clayey materials, alumina-silicates, and the like, may serve as the substrate onto which a vinyl monomer is graft polymerized in the presence of a ceric ion initiator.
It has been considered impossible to prepare graft copolymers containing an inorganic substrate and which are essentially free of homopolymers except with elaborate and impractical processes. By this process, a graft copolymer of a vinyl polymer and an inorganic substrate may be produced.
The resulting product of the process of the present invention may be utilized in many commerical applications either alone or in combination with other compositions. For example, the present graft copolymer product has application as an additive for fluids used in the drilling of subterranean oil and gas wells. In many instances, the polymerization product of the present invention may be further co-reacted with various resins to achieve a wide variety of desired end properties, particularly in the fields of textiles and paper chemistry.